Recent Works on Lichens. A. Lorrain Smith. 199 
and hyphae. He tested over I00 species from various groups 
and has determined in them inorganic salts of phosphorus, 
magnesium, calcium, and nitrogen (ammonium salts with nitrites 
and nitrates). The first four were found in both symbionts; 
nitrites and nitrates were difficult to locate and are probably 
used up as soon as they are formed; phosphorus was more 
abundant in the hyphae than in the gonidia; phosphoric salts 
as small granules, and crystals of magnesium were found in the 
apothecia, or more rarely in the thallus. 
Mameli (1920, 1) tested for the presence of starch in lichens, 
and found it—as we should expect—in or close to the gonidia. 
Starch is a constituent of the green cells alone and can hardly 
be considered as a product of the symbiotic plant. Glycogen 
(1920, 5) she found in the gelatinous substance of the cyano- 
phyaceous algae, it also is the product of one symbiont (see 
West’s “Algae,” p. 14). Amyloid determined by Moreau in the 
hymenial tissues has been proved by her to be an insoluble 
substance. 
Bioret (1921) noted in the apothecia of Graphis sp. large 
quantities of minute refractive bodies distributed through the 
hymenial tissues. He concluded finally that these were oil- 
drops, and suggests that their function may be to preserve the 
hymenium from excessive desiccation. 
E. J. Fry (1922) discusses the significance of oil in limestone 
endolithic lichens. She concludes that: “there is probably some 
relation between growth, evolution of carbon dioxide, oil forma- 
tion, and solution of the limestone.’’ She agrees with other 
workers that the oil is not a storage of reserve food but is waste 
material produced under adverse conditions during the evolu- 
tion of carbon dioxide. She finds further that the boring action 
of the lichens is brought about by the carbon dioxide of respira- 
tion dissolved in water. 
Ethel Mellor (1921 and 1922) has described the action of 
lichens on glass, and finds as did Gaston Buchet that they may 
seriously damage church windows. She has identified from the 
windows 22 lichens, one of which with its variety (Caloplaca 
vitricola and var. violacea) is new to science. The conclusions 
she comes to are:—The immediate cause of corrosion of the 
glass is the mechanical action of the lichens on glass which has 
already been chemically altered by moisture, glass having an 
affinity for humidity in which carbon dioxide from the air is 
dissolved; the silicates become more or less hydrolysed, with 
formation of silicic acid and hydrates of calcium and sodium; 
the lichen hastens the alteration that had already commenced, 
burrowing into the glass and excavating small flakes. The glass 
coloured yellow resists corrosion a long time. 
